Project V proposes both fundamental studies of the interaction of laser energy with dentin and the application of lasers to promote increased adhesion between dentin and of restorative polymers. It is hypothesized that physical and chemical surface modifications of dentin can be induced by the family of X:YAG (yttrium-aluminum-garnet) lasers in which X is Nd, Er, or Ho. These modifications will be designed to provide better adhesion by means of micromechanical interlocking and/or primary chemical bond formation of restorative materials and dentin. In order to evaluate this hypothesis we will carry out the following specific aims: 1) determine light absorbance characteristics of dentin in a variety of surface conditions to optimize laser wavelength; 2) modify standardized dentin surfaces using Nd:YAG; Ho:YAG; and Er:YAG lasers and evaluate physical and chemical changes as function of the energy and power parameters of each laser; 3) identify, through a series of screening tests, those modifications which are beneficial for adhesion to dentin; 4) characterize promising modifications using appropriate analytical techniques including: scanning electron microscopy with energy and wavelength dispersive x-ray microanalysis, Fourier transform infrared spectroscopy, x-ray diffraction, high resolution and analytical transmission electron microscopy, x-ray photoelectron microscopy, Auger electron spectroscopy and secondary ion mass spectroscopy. The depth of surface modification and the differences as a function of dentin variation will be explored. To model and evaluate the clinically achievable bond strengths. modified dentin surfaces will be bonded to currently available dental materials, using a model system to simulate perfusion pressure and fluid effects on bonding in situ.